This is bad and hints at a bigger problem:
The Taiwanese Ministry of Defense released news on Oct. 26 saying that a military major sold secrets about American aircraft to mainland China. The major is now under investigation, along with over a dozen others suspected of involvement, Taiwanese authorities said. ...
Ting Shou-chung, a lawmaker with the incumbent National Party, said that the leak will have a severe impact on Taiwan’s air defenses.
“It not only creates a significant loophole in national defense, but also impacts on military trade between the U.S. and Taiwan,” he said in an interview with Voice of America. Ting continued: “The U.S. will be less willing to sell us high-tech weapons, in case it is leaked to mainland China.”
Yes. If we think Taiwan is a conduit to China for US technology, we won't sell weapons as advanced as Taiwan might like--and need--to fight China.
And if we think China can conquer Taiwan (or agree to be absorbed by China), we will not want to sell Taiwan advanced weapons that China will simply capture and examine at their leisure.
Unless Taiwan starts building their own advanced weapons, their failure to build a military capable of using advanced weapons to actually hold their ground will mean that they will have less access to advanced weapons to hold their ground.
That's a real death spiral.